CHAPTER II. THE CONSTRUCTION OF SIMPLE TOY ELECTRIC MOTORS.
The Simplex Motor is an interesting little toy which can be made in a couple of hours, and when finished it will make an instructive model.
As a motor itself, it is not very efficient, for the amount of iron used in its construction is necessarily small. The advantage of this particular type of motor and the method of making it is that it demonstrates the actual principle and the method of application that is used in larger machines.
FIG. 8.—Details of the Armature for the Simplex Two-pole Motor.
The field of the motor is of the type known as the "simplex" while the armature is the "Siemen’s H" or two-pole type. The field and the armature are cut from ordinary tin-plated iron, such as is used in the manufacture of tin cans and cracker boxes.
The simplest method of securing good flat material is to get some old scrap from a plumbing shop. An old cocoa tin or baking-powder can may, however, be cut up and flattened and will then serve the purpose almost as well.
FIG. 9.—Showing the Armature assembled on the shaft ready for winding.
The Armature—Two strips of tin, one-half of an inch by one and one-half inches, are cut to form the armature. They are slightly longer than will actually be necessary, but are cut to length after the bending operations are finished. Mark a line carefully across the center of each strip. Then taking care to keep the shape symmetrical so that both pieces are exactly alike, bend them into the shape shown in Figure 8. The small bend in the center is most easily made by bending the strip over a knitting-needle and then bending it back to the required extent.
FIG. 10.—A front view of the Field Frame.
A piece of knitting-needle one and seven-eighths inches long is required for the shaft. Bind the two halves of the armature together in the position shown in Figure 9. Bind them temporarily with a piece of iron wire and solder them together. The wire should be removed after they are soldered.
FIG. 11.—The completed Field Frame, ready for winding.
The Field Magnet is made by first cutting out a strip of tin five-eighths of an inch wide by five inches long and then bending it into the shape shown in Figure 11. The easiest way of doing this with the most accuracy is to cut out a piece of wood as a form, and then bend the tin over the form. The dimensions shown in Figure 10 should be used as a guide when making the form.
FIG. 12.—The Bearings.
Two small holes should be bored in the feet of the field magnet to receive No. 8 wood screws, the purpose of which is to fasten the field to the base.
The Bearings are shown in detail in Figure 12. They are easily made by cutting from sheet tin. Care should be taken to make the bearings accurately so that the armature will be in the proper position when the motor is assembled. Two small washers, serving as collars, should be soldered to the shaft as shown in Figure 13.
The Commutator Core is formed by cutting a strip of paper three-eighths of an inch wide and about five inches long. It should be given a coat of shellac on one side and allowed to dry until it gets sticky. The strip is then wrapped around the shaft until its diameter is three-sixteenths of an inch. The sticky shellac should be sufficient to hold the paper tightly in position when dry.
The Base is cut from any ordinary piece of wood and is in the form of a block about two and one-half by one and seven-eighths by one-half inches thick.
FIG. 13.—Side view of the Armature and Commutator Core assembled on the Shaft before winding.
Assembling the Motor—The parts must be carefully prepared for winding by covering with paper. Cut a strip of paper five-eighths of an inch wide and one and three-eighths inches long and give it a coat of shellac on one side. As soon as it becomes sticky, wrap it around one of the two upper vertical parts of the field magnet as indicated in Figure 11. Both sides of the field should be insulated with paper in this manner. The armature is insulated in exactly the same way, taking care that the paper covers the entire flat portion.
The field and armature are now ready for winding. It is necessary to take proper precautions to prevent the first turn from slipping out of place.
The field should be wound first. This is accomplished by looping a small piece of tape or cord over it at the point indicated by "A" in Figure 15. The next two turns are then taken over the ends of the loop so as to embed them. Wind on three layers of wire on one side and then run the wire across to the other side and wind on three layers there. The third layer of wire in the second coil should end at "B." It should be fastened into position by a loop of string so that it will not unwind.
FIG. 14.—Showing the Motor assembled on the Base so that all the parts may be lined up before winding.
This method divides the field winding into two parts, both of which are connected together. The outside layer of the first coil is connected to the inside layer of the second coil. The two coils really form one continuous winding divided into two parts. After the winding is finished, give it a coat of shellac.
The winding of the armature is somewhat more difficult. The wire used for winding both the armature and the field should be No. 25 or No. 26 B. & S. Gauge double cotton-covered.
FIG. 15.—The Field Frame with the Winding in position.
In order to wind the armature, cut off about seven feet of wire and double it back to find the center. Then place the wire diagonally across the center of the armature so that there is an equal length on both sides. Place a piece of paper under the wire at the crossing point to insulate it. Then, using one end of the wire, wind four layers on half of the armature. Tie the end down with a piece of thread and wind on the other half.
The ends of the wire are cut and scraped to form the commutator segments. Figure 17 shows how this is done.
FIG. 16.—The Armature Winding before the Commutator is completed.
Bend the wires as shown so that they will fit closely to the paper core. Bind them tightly into position with some silk thread. Use care so that the two wires do not touch each other. Cut the free ends of the wire off close to the core.
When finished, the relative positions of the armature and the commutator should be as shown in Figure 17.
Figure 14 shows how the motor is assembled. The windings are not shown for the sake of clearness. The armature should be exactly in the center of the field. The bearing holes should be in the correct position and should permit the armature to revolve freely.
FIG. 17.—The completed Armature showing how the Commutator is constructed.
The armature should not scrape against the field at any point, but should clear it by about one-sixteenth of an inch.
The brushes are made by flattening a piece of wire by a few light hammer blows.
The brushes are fastened under a small clamp formed by a strip of tin held down at each end with a wood screw. They can be adjusted to the best advantage only under actual working conditions when the current is passing through the motor. One or two dry cells should be sufficient to operate the motor.
The completed motor is shown in Figure 19.
One end of the winding is connected to one of the brushes. The other brush and the other end of the field form the terminals to which the battery is connected.
The motor, being of the two-pole armature type, must be started when the current is turned on, by giving it a twist with the fingers.
FIG. 18.—Details of the Commutator.
Put a drop of oil on the bearings, make sure that the brushes bear firmly but not tightly against the commutator, connect the battery and your motor is ready to run. It will spin at a high rate of speed.
FIG. 19.—The completed Motor.